Currently, various manufacturing operations require the extrusion of thermoplastic liquids, such as hot melt adhesives, from slot-shaped openings in nozzles. For example, it may be desirable to lay down a thin film of adhesive on a moving substrate, such as a nonwoven material. The thin film of adhesive may have any desired width but, for example, one application requires a total width of 150 mm. In addition, it may also be desirable to have different add-on weights of adhesive along the length of the substrate as the substrate moves adjacent to the dispenser during the manufacturing operation. In one current design, a shim plate construction is used which includes three adjacent 50 mm slots to achieve a total dispensed adhesive width of 150 mm. Each 50 mm slot is fed by two separate on/off valve modules which receive pressurized liquid adhesive from two separate pumps. For example, a system such as the one disclosed in U.S. Pat. No. 6,422,428 may be used in this situation. The disclosure of U.S. Pat. No. 6,422,428 is hereby incorporated by reference herein. The difference between the system disclosed in U.S. Pat. No. 6,422,428 and the slot coating system just described is that a slot coating nozzle assembly extends across multiple valve modules as opposed to having a separate nozzle coupled to each module as shown in the patent.
In the current slot coating system, to achieve different add-on weights along the length of the dispensed film, one of the two valve modules feeding a 50 mm slot is cycled off and then on again. The other valve module feeding that slot remains on. While one of the two valve modules is off, a lesser amount of liquid should theoretically flow to the 50 mm slot and be discharged. This system, however, did not produce the desired results in that the patterns produced were not controllable in an acceptable manner and with the accuracy of the desired controllable and variable add-on weight of adhesive along the length of the substrate.
For these reasons, as well as others, it would be desirable to provide a dispensing system which allows accurate, individually metered output capability from a single extrusion location on a dispensing system.